This invention relates to methods and apparatus for the location and concentration of polar analytes using an alternating electric field.
A recent trend in the field of analytical instrumentation has been the development of integrated microfluidic devices in which multiple operations are performed on a single device, e.g., Harrison et al., xe2x80x9cMicromachining a Miniaturized Capillary Electrophoresis-Based Chemical Analysis System on a Chip,xe2x80x9d Science, 261: 895 (1992). Such devices offer many advantages over conventional analytical formats including the ability to handle very small volumes; ease and economy of device fabrication; the ability to integrate multiple operations onto a single integrated device; and the opportunity to achieve a high degree of automation.
In many chemical and biochemical analysis methods performed using microfluidic devices, it is advantageous to concentrate an analyte as part of the analysis. For example, increased analyte concentration generally leads to increased chemical reaction rates, increased rates of mass transfer, and enhanced detectability. However, because conventional concentration methods require a solid phase pullout step (e.g., adsorption), or a phase change of the analyte (e.g., precipitation), or a phase change of the solvent (e.g., evaporation), these methods are not well adapted for use in a microfluidic device.
In addition, methods for controlling the location of an analyte are important in the design of methods using microfluidic devices. For example, prior to a separation step, it may be desirable to locate a sample volume in a spatially-defined injection zone.
Therefore, it would be desirable to have a method for the location and concentration of an analyte that is well suited for use in integrated microfluidic systems.
The present invention is directed towards our discovery of methods and devices for the location and concentration of polar analytes using an alternating electric field.
In a first aspect, the present invention provides a method for the concentration of a polar analyte comprising the steps of effecting the relative translation of the polar analyte and an alternating electric field along a translation path such that a portion of the polar analyte is trapped and concentrated in a concentration zone formed by the intersection of the translation path and the alternating electric field.
In a second aspect, the present invention provides a device for the concentration of a polar analyte comprising a translation path, a first set of electrodes located to provide a first electric field effective to cause the electrokinetic translation of a polar analyte along the translation path, and a second set of electrodes located to provide an alternating second electric field intersecting the translation path and sufficient to trap and concentrate a portion of the polar analyte in a concentration zone formed by the intersection of the translation path and the alternating second electric field.
It is a first object of the invention to provide a method for the concentration of a polar analyte that does not require a solid-phase pull-out step or a phase change of the polar analyte or a solvent.
It is a second object of the invention to provide a method for the manipulation or location of a polar analyte that does not require a solid-phase pull-out step or a phase change of the polar analyte or a solvent.
It is a third object of the invention to provide a method for the concentration or manipulation of a polar analyte that does not require manual intervention and is therefore well suited to automation.
It is a fourth object of the invention to provide a method for the concentration or manipulation of a polar analyte that is well suited for use in a microfluidic device.
The present invention will become better understood with reference to the following written description, drawings, and appended claims.